The invention relates to a casing centralizer. This application is a Continuation-In-Part of PCT/GB98/00554 to which filing details have not yet been assigned by the USPTC.
When a well has been drilled for the eventual production of hydrocarbons, one of the procedures commonly employed in readying the well for production comprises installing hollow tubular casing in the well to line the borehole. The space between the exterior of the casing and the sides of the borehole are filled with cement, which acts as a sealant and provides mechanical support for the casing. As it is desirable that the casing be centralized in the well bore when cemented, proposals have been made for providing the casing (prior to cementing) with externally mounted centralisers to hold the casing away from the well bore and towards the centre of the bore.
longitudinally therethrough, the annular body being formed from at least one material selected from the group consisting of plastic material, elastomeric material and rubber material, the substantially cylindrical bore being a clearance fit around the tubular casing to be centralised by the centralizer.
In a preferred embodiment the invention provides a casing centralizer assembly comprising tubular casing and a centraliser as defined above.
Typically, the plastic, elastomeric and/or rubber material may comprise polytetrafluoroethylene (PTFE), polyetheretherketone, carbon reinforced polyetheretherketone, polyphthalamide, polyvinylidene fluoride, polyphenylylene sulphide, polyetherimide, polyethylene, polysulphone, polyethersulphone, polybutyleneteraphthalate, polyetherketoneketone, polyamides, a rubber and rubber compounds, phenolic resins or compounds, thermosetting plastics, thermoplastic elastomers, thermoplastic compounds or thermoplastic polyester resins.
In one example of the invention, the plastic, elastomeric or rubber material may contain a filler material, such as glass, carbon, PTFE, silicon, molybdenum disulphide, graphite, oil or wax, or any combination of these materials.
The annular body may be manufactured from and consist of the plastic, elastomeric and/or rubber material. However, the annular body may comprise a combination of the plastic, elastomeric and/or rubber material and another material such as a metal. For example, the annular body may comprise a metal skeleton or other structure coated, or partially coated, with the plastic, elastomeric or rubber material. In addition, or as an alternative, the annular body may comprise a combination of different plastic, elastomeric and/or rubber materials.
The annular body may be formed in one or more sections which may be assembled around the tubular to be centralised by the centralizer. In one embodiment the annular body is divided into 2 sections along its axis so that each section forms a xe2x80x9chalf shellxe2x80x9d arrangement. The concave surface of one section can be fitted direct against one side of the outer surface of the tubular and connected to another section similarly positioned against the opposite side of the tubular. The 2 sections can then be connected around the tubular to make up the centralizer so that it does not need to be offered up to the end of the tubular. This can be very useful in coil tubing applications.
The division between the sections need not be axial.
In some embodiments the sections can be hingedly attached to one another. In others the 2 sections can be separate. There can be more than 2 sections provided. It is sufficient that the sections are adapted to allow the centraliser to be placed around the tubular without needing to be threaded over an end of the tubular.
The sections are preferably held together by fixings and/or hinges. Preferred fixings include bolts but catches and locks can also be used.
Preferably the centraliser further comprises a peripheral array of a plurality of longitudinally extending blades circumferentially distributed around said body to define a flow path between each circumferentially adjacent pair of said blades, each said flow path providing a fluid flow path between longitudinally opposite ends of said centralizer, each said blade having a radially outer edge providing a well bore-contacting surface.
Said centralizer is preferably free of any means tightly gripping a casing when said centralizer is installed thereon, whereby said centralizer and said casing are mutually rotatable.
Said blades are preferably mutually substantially equidistantly distributed around said body. Said blades preferably each extend circumferentially at least part-way around said body between longitudinally opposite ends thereof to provide a circumferential distribution of each said well bore-contacting surface. Each said blade preferably has a radially inner root integral with said body, each said radially inner root preferably being circumferentially wider than the respective radially outer edge. Said blades are preferably circumferentially wider at one end of the centralizer than at the other end, said one end preferably the lower end of the centralizer in use thereof. Said centralizer preferably has five of said blades.
Longitudinally opposite ends of said blades and/or of said body may be chamfered or tapered whereby to facilitate passage of said centralizer down a well bore.